The use of a semipermeable membrane to effect the separat of a gaseous mixture into its various component parts, or at least enriched fractions of the same, has long been known. The development of semipermeable membranes for this purpose is well summarized in columns 4-6 of U.S. Pat. No. 4,230,463. This patent describes in detail multicomponent membranes and discloses a plurality of organic polymers for use as the porous separation membrane including polysulfone, copolymers of styrene and acrylonitrile, polycarbonate and cellulose acetate. Coating materials also include a variety of polymers such as polysiloxane, polyisoprene, alpha-methylstyrene and polysiloxane copolymers and polystyrene. The multicomponent membrane can be employed to separate selectively at least one gas such as hydrogen from a mixture containing two or more of the following gases: hydrogen, carbon monoxide, carbon dioxide, helium, nitrogen, oxygen, argon, hydrogen sulfide, nitrous oxide, ammonia and C.sub.1 to C.sub.5 hydrocarbons.
In addition to the foregoing membranes, others are known for this purpose including those described in U.S. Pat. Nos. 3,350,844 and 3,899,309. While most, if not all, of these membranes show effectiveness in their intended use, none are completely satisfactory. Generally, the membranes used for these separations lack either one or more of desirable flux, selectivity and life and thus industry continues to search for alternatives.
Of particular interest to the chemical processing industry are membranes showing good characteristics for separating carbon dioxide and/or hydrogen sulfide from hydrocarbon streams, typically natural gas, and oxygen enrichment from air. Commercially, these processes do not employ membranes but rather absorption techniques in the former and cryogenic techniques in the latter. Both of these techniques are energy intensive and consequently expensive to operate. Accordingly, there exists the need for identifying and implementing alternative processes and those employing membrane technology appear at this time to offer significant economic advantages. However, to date no membrane has been identified as completely suitable for either one of these processes.